The present invention relates to a structure for attenuating torsional vibration in compressors employed in, for example, air conditioners for vehicles.
A typical compressor, for example, a swash plate type compressor includes a housing in which a crank chamber is defined. The compressor also has a drive shaft, which extends through the crank chamber and is rotatably supported by the housing. A swash plate is fixed to the drive shaft to integrally rotate with the shaft. A cylinder block, which constitutes a part of the housing, has cylinder bores. A piston is reciprocally housed in each cylinder bore. The pistons are operably coupled to the swash plate and are reciprocated by the rotation of the swash plate. The reciprocation of the pistons compresses refrigerant gas in the cylinder bores.
The drive shaft is coupled to an external drive source such as a vehicle engine by an electromagnetic clutch and a belt. The clutch selectively connects and disconnects the external drive source and the drive shaft. The clutch includes a pulley rotatably supported by the compressor housing, an inner hub secured to the distal end of the drive shaft, an armature facing the pulley, and a solenoid. The armature is coupled to the inner hub by leaf springs and is actuated by the solenoid. The solenoid causes the armature to be pressed against the pulley. In this state, the power of the drive source is transmitted to the drive shaft by a belt, the pulley, the armature, the leaf springs and the inner hub.
During operation of the compressor, the compressing action of the each piston results in a compression reaction force that acts on the drive shaft by way of the piston and the swash plate. The compression reaction acts against the rotation of the drive shaft. The magnitude of the reaction fluctuates periodically. This, in turn, generates torsional vibrations of the drive shaft. When transmitted to the armature by the inner hub and the leaf springs, the torsional vibrations are somewhat attenuated by the leaf springs, which have elasticity. However, since the leaf springs are originally designed to function best as a part of the electromagnetic clutch, the leaf springs cannot attenuate the torsional vibration satisfactory.
The drive shaft, the swash plate and the electromagnetic clutch, which rotate integrally, constitute a rotating body having a natural frequency. A torsional vibration occurs in the rotating body. If the frequency of the torsional vibration is equal to the natural frequency of the rotating body, resonance occurs in the rotating body. The resonance amplifies the torsional vibrations by a great degree. The torsional vibrations also fluctuate the torque acting on the drive shaft and the rotational speed of the pulley. Further, the torsional fluctuations ultimately vibrate other engine accessories that are connected with the compressor by a belt. Accordingly, noise in the passenger compartment is increased.
Strong torsional vibrations cause the armature and the pulley to slide relative to each other, which results in poor transmission of power between the power source and the drive shaft. In order to improve the power transmission, the friction between the armature and the pulley needs to be increased. That is, a larger solenoid needs to be employed. A larger solenoid increases the size of the compressor and manufacturing cost.
Japanese Unexamined Patent Publication No. 55-20908 discloses a compressor having a mechanism for attenuating vibrations. The mechanism is located in an electromagnetic clutch and includes a damper and a connecting plate. The damper and the connecting plate couple an armature to an inner hub. The inner hub and the connecting plate are coupled to each other by springs located in their circumferential portions. The inner hub and connecting plate each have serrated surface facing each other. The damper is located between the serrated surfaces.
Torsional vibrations in a rotating body, which includes a drive shaft, change torque applied to the drive shaft and cause the inner hub to slightly slide relative to the connecting plate. The damper between the inner hub and the connecting plate attenuates the vibrations.
The vibration attenuating mechanism is located in the clutch, more specifically, between the armature and the inner hub, which transmit power. However, it is extremely difficult to design the clutch such that the original function of the clutch, which is to selectively transmit power, is not hindered by the attenuating mechanism. Further, the facing surfaces of the inner hub and the connecting plate are serrated, and the springs are used to couple the inner hub with the connecting plate. The serrated surfaces and the springs complicate the structure of the clutch and increase the number of parts. Accordingly, the manufacture of the clutch is burdensome and costly.